Dual or single?

From the below memory which would you choose? Is dual worth the price, or should I OC a little more and get the PC-3500? This is for the family computer, not my work computer. I'm guessing 512 should be enough for now.

Thanks.
KV

Mushkin Blue Dual Pack 184 Pin 512MB(256MBx2) DDR PC-3200
Cas Latency: 2.5-4-4

GeIL DDR RAM 512MB PC-3500 433Hz ULTRA Platinum (single stick)
CAS 2 6-3-3 1T

Geil Ultra Series Value Dual Channel 184 Pin 512MB(256MBx2) DDR PC-3200
Cas Latency: 2.5 7-4-4

Kingson 512mb (2x256mb) DDR400 PC3200, Model KVR400X64C3AK2/512
Latency: CAS Latency 3

Mushkin 184 Pin 512MB DDR PC-3200
Cas Latency: 2.5-4-4